RU2773278C1 - Method for measuring the movements of the stamp image in digital autocollimators and a device for its implementation - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: invention relates to measuring technology and can be used in optical instrumentation, precision engineering, metrology. The method for measuring the movements of the stamp image in digital autocollimators includes the formation of a stamp image in the form of a raster of N+1 transparent parallel slits with a monotonous discrete change in their widths, identification of the image of the stamp slits on the receiver, determination of the slit in the stamp, the angle of incidence of rays from which on the reflector relative to its normal is closest to 0, determination of the reversal angle of the reflector by the position of the center of gravity of the image of this slit on the receiver, correction of the found angle of rotation of the reflector using the correction, determined by the individual geometric and aberration parameters of the autocollimator lens.

EFFECT: multiple expansion of the measurement range of a single-coordinate autocollimator with a simultaneous multiple reduction in the systematic measurement error.

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Description

The group of inventions relates to measuring technology and can be used in optical instrumentation, precision engineering, metrology.

The traditional scheme of an autocollimator for determining the angular position of an object contains an illuminator, a mark located in the focal plane of the lens, a beam splitter, a lens, a control reflective element (reflector) in the form of a flat mirror or a reflecting prism located on the controlled object, a photoelectric receiver in the form of a CCD array or CCD matrix, located in a plane conjugated with the plane of the mark [1].

The measurement of the angular displacement of the reflector relative to the sighting axis of the autocollimator is carried out by registering the shift of the center of gravity of the image of the mark in the plane of the receiver relative to the position of its photosensitive pixels.

Some applications require angle measurements in only one coordinate. In this case, it is more expedient to use a CCD array as a receiver, which has higher speed and reliability, lower heat generation and thermal distortions of the geometry of the photosensitive device during measurements, shorter measurement readiness time, a simpler information processing algorithm, and also has, in comparison with CCDs, -matrix lower cost.

The main parameters of the autocollimator: the range and accuracy of angular measurements, are interrelated and depend on the focal length of the lens, its aberrations, the diameter of the entrance pupil, the size of the receiver pixels, and the distance to the mirror. Generally, the wider the range, the greater the allowable measurement error. However, to solve some practical problems, a universal wide-range autocollimator with increased measurement accuracy in the central part of the range is required. Such an autocollimator can have a lens with a discrete change in focal length to implement two modes of operation: preliminary focusing on a reflector in a wide range through a short-focus lens and final focusing with a high accuracy of angular measurements through a long-focus lens [2], or a relatively short-focus lens to implement a wide measurement range . In this case, to improve the accuracy characteristics, a special brand shape and an algorithm for processing measuring signals [3], or a long-focus lens that provides high measurement accuracy in a relatively small range, are used, and to expand the measurement range, a reflector in the form of a polyhedral mirror [4] or a long-focus lens is used. and a reflector in the form of a corner reflector with a small deviation of one of the dihedral angles from 90° and an additional reflective coating on the front face of the prism, upon reflection from which autocollimation images of the mark are formed in the receiver plane with different coefficients for converting the angular displacement into a linear one [5].

The listed options have a number of disadvantages: the complexity of the constructive implementation of the autocollimation device as a whole or its components, or the low accuracy of measurements, including in the center of the angular range.

A known method of measuring the movement of the brand image, selected as a prototype for the problem being solved [US Pat. RF No. 2602414, IPC G01B 11/26, G02B 27/30, prior. 06/10/2015], which includes the formation in the plane of the multi-element radiation receiver of the image of the brand in the form of a line raster, the width of the side strokes of which is chosen equal to the width of the elements of the radiation receiver, and the width of the central stroke is chosen equal to twice the width of the remaining strokes of the raster, then the signals from the illuminated elements are measured , memorizing them, fixing the element on which the signal is absent, based on the obtained data, the approximate movement of the mark is calculated, the position of the energy center of gravity of the image of the line raster is determined, and, taking into account the position of the energy center of gravity, the amount of movement of the mark image is determined. The technical result consists in increasing the accuracy by increasing the measurement range and simplifying the design of the device.

The problems of the described method are:

- a high probability of information loss due to the high spatial frequency of the line raster, which, with an increase in the measured angle and (or) distance to the reflector, taking into account the finite aberrations of the real lens, can lead to "floating" ¹ ( ¹ By the term "floating" we mean an excess of the magnitude of signals with sensitive elements of the line of some predetermined threshold level.) gaps between the signals of the receiver, and hence to distortion or complete loss of information about the position of the screened pixel;

- a small range of measurement of movement of the image of the brand, limited by the condition of "non-exit" of the image of the shaded area of the image of the brand beyond the CCD line;

- discrepancy between the measured movement of the mark and the true angle of rotation of the reflector due to finite aberrational distortions of the mark image by a real lens at large measured angles and distances to the reflector, i.e. the measurements themselves are incorrect.

Known photoelectric autocollimation device, selected as a prototype for the problem being solved (USSR author's certificate No. 1737264A1, IPC G01B 11/26, prior. 04/05/1990). The device includes an illuminator optically coupled to a photodetector through intermediate flat and annular mirrors, a slit diaphragm, made in the form of a set of slit diaphragms located on both sides of the central slit diaphragm and having different widths, by δ and Δ relative to the central diaphragm, the main lens placed a reflective element, an additional lens and two intermediate flat mirrors on the controlled object. The step between the centers of the slit diaphragms is made in such a way that the step between the centers of the images of the diaphragms on the ruler is slightly smaller than the size of the CCD ruler. In the initial position, the central slit diaphragm is projected onto the receiver line in the center (on the central receiving element). The CCD polling unit and the electronic unit in the form of a microprocessor process the received signals from the CCD array and register the position of the aperture image with high accuracy. When the controlled object misaligns with the optical device for monitoring its position, the image of the central slit diaphragm is proportionally shifted along the line of the CCD photodetector, which, at a certain amount of mismatch, will exceed the geometric length of the line. But at the moment the image of the central slit diaphragm leaves the photosensitive line of the CCD receiver, an image of the first additional slit diaphragm will appear at its other end. If the image of the first additional diaphragm goes beyond the line of the receiver, then the image of the second additional diaphragm will appear. The interrogating block of the CCD-line and the microprocessor identify and calculate the distance between the images of the diaphragms and, taking them into account, give the results of determining the angle of rotation of the reflector. All this increases the sensitivity of the device by 30%, and the limits of the controlled reflector (object) displacement parameter are doubled.

The problems of the described device are:

- significant errors in determining the angle of rotation of the reflector from the image coordinates of only one of the set of slit diaphragms, taking into account the finite aberrations of the lenses;

- the complexity of the design as a whole due to a significant number of optical elements at a distance from the slit diaphragm to the CCD receiver, leading to an increase in the positioning error of the brand image on the receiver even with very slight (individually) variations in the positions of the elements in the optical path (for example, due to inevitable temperature fluctuations body geometry).

In the process of research, I found that the use of a brand in the form of a raster of N + 1 transparent slits with a uniform distribution of their centers along the brand and a monotonous discrete change in their widths, for example, by the width of a CCD line pixel, allows you to select from individual images of the brand slits on the receiver image is the least distorted by lens aberrations, the position of the center of gravity of which on the CCD ruler most closely matches the angle of rotation of the reflector. To implement this, it is necessary: to choose the minimum width of the slit and the distance between adjacent slits several times greater than the pixel size, and the total size of the raster of slits is approximately equal to the size of the ruler;

- to identify images of slits on the CCD ruler and determine the specific slit on the stamp, the light rays from which fall on the reflector with a minimum angle relative to its normal;

- extract from the general image of the brand on the receiver the image from the found specific slot;

- use the shift of the selected image on the PS3 ruler as an indicator of the angle of rotation of the reflector.

Using the selected image on the CCD ruler to determine the angle of rotation of the reflector using a corrective correction determined by the individual geometric and aberration parameters of the autocollimator lens, it is possible to significantly (several times) increase the range of angular measurements of the autocollimator compared to an autocollimator with a mark from a single slit, and significantly (several times) reduce the error in determining the angle of rotation of the reflector over the entire range of angular measurements.

The problem to be solved by the claimed group of inventions is to increase the range of single-coordinate angular measurements and ensure high measurement accuracy.

The tasks are solved by

- in the method, including the formation of the image of the brand in the form of a raster of strokes in the plane of a multi-element radiation receiver, the novelty is that the brand is selected in the form of a raster of N + 1 transparent parallel slots with a monotonous discrete change in their widths, the width of the raster is chosen no more than the size of the CCD; rulers, the minimum width of the slit and the distance between adjacent slits are chosen several times greater than the pixel size of the CCD ruler, the images of the brand slits ^{on the} CCD ruler are identified .), according to the positions of the centers of gravity of the images of the slots for each k-th image of the slot of the brand, the approximate angle ϕ _k of the turn of the reflector is calculated by the formula:

where:

δ _k - shift of the k-th slot in the brand relative to its center, mm;

CG _k - position of the center of gravity of the image ³ ( ³ Approaches to determining the CG of the image on the ruler are known.) k-th slit on the CCD ruler relative to its center when the reflector is turned at an angle ϕ relative to the sighting axis of the AK, mm;

F - focal length of the AK lens, mm;

, по величине сдвига δ_i, ближайшей к произведению F tan

, определяют i-ю щель в марке, угол падения световых лучей от которой на отражатель относительно его нормали наиболее близок к 0, вычисленное в соответствии с (1) значение угла ϕ_i для найденной щели марки используют в качестве величины измеренного угла, для уточнения этой величины применяют корректирующую поправку, определяемую индивидуальными геометрическими и аберрационными параметрами объектива автоколлиматора;for the calculated approximate angles of turn of the reflector, the average value of the angle is determined

, according to the shift value δ _i , closest to the product F tan

, determine the i-th slot in the brand, the angle of incidence of light rays from which on the reflector relative to its normal is closest to 0, calculated in accordance with (1) the value of the angle ϕ _i for the found slot of the brand is used as the measured angle value, to refine this the values apply a corrective correction determined by the individual geometric and aberration parameters of the autocollimator lens;

- in a device containing an illuminator, a brand in the form of a raster of slit diaphragms, a lens, a reflector installed on a controlled object, a CCD array, a CCD interrogation unit and an electronic unit, what is new is that the raster of slit diaphragms is selected in the form of a raster from N + 1 transparent parallel slits with a monotonous discrete change in their widths, the raster size is chosen no more than the size of the CCD line, the minimum width of the slit and the distance between adjacent slits are selected several times greater than the pixel size of the CCD line, the CCD interrogator and the electronic unit are made in the form of a control unit and signal processing, which determines the value of the measured angle of rotation of the reflector, taking into account the corrective amendment stored in its memory.

The essence of the invention is illustrated by drawings.

между блок управления и обработки сигналов и ПЗС-линейкой обозначает обмен управляющими и измерительными сигналами.Figure 1 shows a block diagram of an autocollimation device, where a radiation source 1, a condenser 2, a mark 3 in the form of a raster of transparent parallel slits with a monotonous discrete change in their widths, a prism block 4 with a beam-splitting face 5, an objective 6, installed in series along the optical axis, is a radiation source 1, a condenser 2, a reflector 7 mounted on a controlled object, for example in the form of a flat mirror, a multi-element radiation receiver 8, for example, in the form of a CCD-line, a control and signal processing unit 9. Brand 3 and a multi-element radiation receiver 8 are installed in the focal conjugate planes of the lens 6; double arrow

between the control and signal processing unit and the CCD line indicates the exchange of control and measurement signals.

Figure 2 shows a diagram of the autocollimator with drawing the path of rays from transparent slits 1 brand through the lens 2 to the CCD line 3 with intermediate reflection from the reflector 4 normally located relative to the sighting axis of the autocollimator, where the hollow arrows indicate the path of the rays from the central slit of the brand, and solid arrows - path of rays from one of the peripheral slots, F - focal length of the lens, L - distance from the lens to the mirror.

Figure 3 shows a conditional diagram of an autocollimator with drawing the path of rays from transparent slits 1 of the brand through lens 2 to the CCD line 3 with intermediate reflection from a reflector 4 deployed at an angle ϕ, where hollow arrows indicate the path of rays from the central slit of the brand, and solid arrows - beam path from one of the peripheral slots, ϕ - reflector turn angle, S ₀ (ϕ) and S _i (ϕ) - displacement of the centers of gravity of images of the central and i-th slots when the reflector is turned, respectively.

Figures 4, 5, 6 show the results of calculations of systematic errors of angular measurements for the autocollimator described in [7], for two realizations of the brand shape: a single transparent slit (an array of points 1-1) or a raster of transparent parallel slits (an array of points 2- 2 and 3-3), at distances to the reflector of 50, 500 and 1000 mm, respectively.

Figure 7 presents the results of calculations of systematic errors of angular measurements for an autocollimator with a 3-lens telephoto lens, described in [8] (task 19.2), for two realizations of the brand shape: a single transparent slit (arrays of large hollow points 1-1, 2- 2, 3-3 and 4-4 at distances to the reflector of 50, 500, 1000 and 2000 mm, respectively) or a raster of transparent parallel slots (an array of small dots 5-5 for distances to the reflector from 50 to 2000 mm).

The essence of the proposed method for measuring the movement of the brand is as follows. At a small distance to a normally located mirror (L ~ F) (Fig. 2), the rays from the slits of the brand, shown in the figure as pinholes (top view), build images of the slits on the receiver with virtually no distortion, since the rays pass near the center of the lens and at small angles with respect to its axis.

With an increase in the distance L, the rays from the peripheral slits after reflection move to the edge of the lens and the angles of the “kinks” of the trajectories increase during its passage. Aberrations of inclined beams lead to noticeable distortions in the images of the slits of the mark, and in the general case, the farther from the axis the slit is located, the stronger the distortion of its image. Distortions in the image of the central slit remain minimal and virtually independent of distance. Thus, fixing the zero angle of rotation of the mirror should be carried out by analyzing the image of the central slit.

The situation changes when the mirror is turned. Let's say the mirror is rotated relative to the lens axis at an angle ϕ (figure 3). The position of the center of gravity of the image of the central slit is shifted in the plane of the receiver by the value S ₀ (ϕ). As the distance L increases, the rays of the central slit reflected from the mirror shift to the edge of the objective, the aberrations of the inclined beams grow and distort the projection of the slit in the plane of the receiver. This leads to a change in the value of S ₀ (ϕ) and an increase in the measurement error of the angle ϕ. Let us assume that for a given angle ϕ the rays from the ith slit of the brand fall on the mirror normally, i.e. the reflected rays are superimposed on the original ones. Then the trajectories of the passage of rays through the lens weakly depend on the distance to the mirror, and the shift of the slit projection S _i (ϕ) (relative to its conditional initial image in an ideal, aberration-free optical system) remains almost unchanged. Thus, this particular angle ϕ, in terms of the error of its autocollimation measurement, should be determined by analyzing the image of the ith slit in the plane of the receiver, i.e. by displacement S _i (ϕ). At an arbitrary angle of the mirror's turn, it is expedient to carry out measurements by analyzing the image of that of the slits, the angle of incidence of rays from which on the mirror is closest to π/2. Adequate measurement results in the full range of the mirror turn will be obtained with adaptive selection of the image required for analysis from all projections of the slits. It is obvious that in this case the gaps in the stamp should be "colored", i.e. vary in width so that their images are reliably identified in the plane of the receiver. For example, the slit widths of the mark are discretely changed by the pixel width of the ruler. With equidistant position on the mark of the centers of the slots, the distances between the slots also discretely change by the same value, which also contributes to the correct identification of the images of the slots of the mark on the ruler.

We will calculate the characteristics of the autocollimator (AC) using the proposed measurement method for the AC described in [7] with a 7-lens teleobjective with a focal length and an entrance pupil diameter of 142 and 43 mm. A CCD array of 1024 pixels with a width/height along the array of 13/150 μm was used as a receiver in [7]. To measure the angle in the horizontal plane, a single transparent stroke of the brand with a width of 140 µm was used. In the range of angular measurements of ±10', the experimentally measured error did not exceed ±0.7''.

For the parameters of the teleobjective used in the AC, the Monte Carlo method by random ray tracing through all optical elements was used to calculate possible systematic errors in angular measurements due to finite aberrational distortions of light beams when passing through the optical path of the AC with intermediate reflection from a remotely mounted reflector.

The results of modeling the reaction of AK with a brand of 13 transparent strokes with distances between centers of 1 mm, a width of 100 to 220 μm, a sampling step of 10 μm, for different algorithms for processing measuring signals at a distance to the mirror L=50 mm are shown in Fig.4. The reflector is located vertically and rotates in the horizontal plane in the range of ±150' through 1'. The array of points 1-1 reflects the results when processing the image of only the central stroke of the brand and corresponds to the reaction of a typical AK with a brand in the form of a single stroke. An array of points 2-2 correspond to the method of determining the angle with adaptive selection from all projections of the strokes of the i-th stroke required for image analysis, and, accordingly, the desired value of the calculated angle ϕ _i . As can be seen from the figure, in the range of issuing angular information on the image of the central stroke (range of points 1-1), the use of the method with adaptive selection of the image optimal for analysis leads to an approximately tenfold decrease in the systematic measurement error with a simultaneous, almost twofold expansion of the total measurement range (points 2 -2). For partial error correction at the edges of the extended range, an additional correction function can be used. In particular, for a simulated lens, a good result is obtained by replacing in expression (1) the sum of the arc tangents of the arguments by the arc tangent of the sum of the arguments:

The array of points 3-3 of the figure reflects the result of the implementation of the specified correction.

Since, as noted above, the position of the center of gravity of the image of the optimal i-th stroke weakly depends on the distance to the reflector, expression (2) can be used to correct the systematic error at other distances as well. Figures 5 and 6 show the simulation results for distances to the reflector L=500 mm and L=1000 mm, respectively.

With an increase in the distance to the mirror, the gain in terms of the multiplicity of the measurement range expansion when using the adaptive algorithm increases, since due to the vignetting of the backscattered beam, the range of outputting angular information along the central stroke drops from ±79' to ±35'.

The systematic error in processing the image of the central stroke is ±26'', but in the range of ±35' it does not exceed ±7'' for all distances, while in the range of ±10' it is less than ±1'' (which correlates with the AC parameters in [7]), and in the range of ±6' - less than ±0.1''. In the range of ±150', the systematic error of measurements according to the corrected adaptive algorithm for all distances does not exceed ±4''. In the range of ±12', the angular information is determined from the image of the central stroke with the corresponding errors.

Thus, the application of the proposed method for measuring the movements of the brand image allows for the analyzed AK in the range of distances to the reflector from 50 to 1000 mm to expand the range of angular measurements by 150735' ≈ 4.3 times while reducing the systematic error by 2674'' = 6.5 times, while maintaining the original high measurement accuracy in the center of the angular range.

A similar computational simulation was carried out for an AK with a 3-lens telephoto lens with the parameters described in [8] (task 19.2), at a distance to the reflector from 50 to 2000 mm, in the range of angular measurements of ±60' (Fig. 7). The focal length of the lens is 320 mm, the light diameter of the positive gluing of the lenses in the simulation was taken equal to 42 mm, the negative lens - 14 mm. A raster of 27 transparent strokes with a width from 40 to 300 µm with a sampling step of 10 µm and a distance between the centers of the strokes of 500 µm was used as a mark in the simulation. The figure shows the results of simulation of systematic AC errors. Arrays of large hollow dots 1-1, 2-2, 3-3 and 4-4 reflect, respectively, the results of modeling a systematic error with calculations on the central stroke of the brand at a distance to the reflector of 50, 500, 1000 and 2000 mm, an array of small dots 5 -5 reflects the variation of the measurement results at four distances with calculations based on the optimal (using the adaptive algorithm) strokes of the mark.

As can be seen from the figure, for this lens, the results of calculating the angle from the central stroke are closer to the truth at the minimum distance L, however, as it increases, the adaptive algorithm shows more adequate results. Since the typical allowable range of distances to the CE during measurements exceeds at least several times the focal length of the objective, the use of the adaptive algorithm as a whole is also preferable in this case. Let us pay attention to the good agreement between the results of angular calculations by the adaptive algorithm for different distances (differences within 1''), which confirms the earlier conclusion that it is possible to apply a general correction for the adaptive algorithm in order to level the error at the edges of the extended range. The type of correction is determined by the geometric and aberration parameters of the lens, i.e. for each lens it is individual. For this lens, the use of a corrective correction will reduce the systematic error over the entire range to the level of ±0.5".

For an AK with the described 3-lens telephoto lens, the use of the proposed method for measuring the movements of the brand image allows, at a distance to the reflector from 50 to 2000 mm, to expand the range of angular measurements by 60717' ≈ 3.5 times while reducing the systematic error by 7''/0.5 ''=14 times, while maintaining the original high measurement accuracy in the center of the angular range.

Thus, the use of a distributed mark from a raster of transparent strokes, the widths of which change in a known discrete manner, in combination with an adaptive signal processing algorithm, allows us to significantly expand the range of angular measurements of the AC - the multiplicity of the range expansion depending on the distance to the reflector can be up to several times, while providing high measurement accuracy in the central part of the range. The constant character of the systematic error, practically independent of the distance to the reflector, makes it possible to introduce an individual correction for a particular AK lens to reduce the systematic error of angular measurements in an extended range by several times.

Our company has issued a set of working documentation for the manufacture of a high-precision single-coordinate autocollimator with an extended range of angular measurements.

Literature.

1. High-precision angular measurements / Ed. SOUTH. Yakushenkova, M.: Mashinostroenie, 1987. 480 p.

2. Sklyarov S.N., Semenov O.B., Shcheglov S.N. Autocollimation measuring device. Patent of the Russian Federation No. 2491586, prior. from 23.01.2012

3. Soldatov V.P. A method for measuring the movements of the brand image in digital autocollimators and a device for its implementation. Patent of the Russian Federation No. 2602414, priority dated 10.06.2015

4. Burmistrenko V.A., Bogdanovich E.M., Vanyurikhin A.I., Gailish E.P. Device for controlling the accuracy of autocollimators. Author's certificate of the USSR No. 560135, priority dated 07/21/1975.

5. Konyakhin I.A., Vorona A.M. Experimental studies of a wide-range autocollimator // Scientific and technical bulletin of St. Petersburg State University ITMO, issue 18, 2005, pp. 224-227.

6. Pinaev L.V., Tikhomirova N.L., Firsov N.T., Pinaeva T.D., Bakuev A.A. Photoelectric autocollimation device. Author's certificate of the USSR No. 1737264A1, priority dated 04/05/1990.

7. Zhukov Yu.P., Lovchii I.L., Pestov Yu.I., Sergeev V.A., Stradov B.G. Small-sized two-coordinate digital autocollimator // Optical journal, vol. 86, 2019, no. 8, pp. 29-35.

8. Avenko M.I., Zapryagaeva L.A., Sveshnikova I.S. Task book on applied optics: Proc. allowance. - M.: Higher. school, 2003. - 591 p.

Claims (8)

1. A method for measuring the movements of the brand image in digital autocollimators (AC), which consists in the fact that the brand image in the form of a raster of strokes is formed in the plane of a multi-element radiation receiver, for example, a CCD line, characterized in that the brand is selected as a raster from N + 1 transparent parallel slits with a monotonous discrete change in their widths, the raster width is chosen no more than the size of the CCD line, the minimum width of the slit and the distance between adjacent slits are chosen several times greater than the pixel size of the CCD line, the images of the brand slits on the CCD line are identified by positions centers of gravity of the images of slots for each k-th image of the slot of the brand calculate the approximate angle ϕ _k of the turn of the reflector according to the formula

where: δ _k - shift of the k-th slot in the brand relative to its center, mm; CG _k - the position of the center of gravity of the image of the k-th slit on the CCD ruler relative to its center when the reflector is rotated through an angle ϕ relative to the sighting axis of the AK, mm; F - focal length of the AK lens, mm, for the calculated approximate angles of turn of the reflector, the average value of the angle is determined

, according to the shift value δ _i , closest to the product F tan

, determine the i-th slot in the brand, the angle of incidence of light rays from which on the reflector relative to its normal is closest to 0, the value of the angle ϕ _i calculated in accordance with the formula for the found slot of the brand is used as the value of the measured angle, to refine this value, apply corrective correction determined by the individual geometric and aberration parameters of the autocollimator lens. 2. A device for measuring the movement of the brand image in digital autocollimators, containing an illuminator, a brand in the form of a raster of slit diaphragms, a lens, a reflector mounted on a controlled object, a CCD ruler, a CCD interrogation unit and an electronic unit, characterized in that the raster of slit diaphragms is selected in the form of a raster of N + 1 transparent parallel slits with a monotonic discrete change in their widths, the raster size is chosen not to exceed the size of the CCD line, the minimum slit width and the distance between adjacent slits are chosen to be several times greater than the pixel size of the CCD line, the CCD interrogator and the electronic unit is made in the form of a control and signal processing unit that determines the value of the measured angle of rotation of the reflector, taking into account the corrective correction stored in its memory.

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